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Fatigue
| ICD10 = | ICD9 = | ICDO = | OMIM = | DiseasesDB = 30079 | MedlinePlus = | eMedicineSubj = | eMedicineTopic = | MeshName = Fatigue | MeshNumber = C23.888.369 | }} Fatigue (also called exhaustion, lethargy, languidness, languor, lassitude, listlessness or tiredness) is a state of awareness describing a range of afflictions, usually associated with physical and/or mental weakness, though varying from a general state of lethargy to a specific work-induced burning sensation within one's muscles. Physical fatigue is the inability to continue functioning at the normal levels of physical activity. It is ubiquitous in everyday life, but usually becomes particularly noticeable during heavy exercise. Mental fatigue, on the other hand, rather manifests in somnolence (sleepiness). Fatigue has two known forms; one manifests as a local, muscle-specific incapacity to do work, and the other manifests as an overall, bodily or systemic, sense of energy deprivation. Due to these two divergent facets of fatigue symptoms, it has been proposed to look at the causes fatigue from "central" and "peripheral" perspectives (Gandevia, 1992; Kent-Braun, 1999). Fatigue can be dangerous when performing tasks that require constant concentration, such as driving a vehicle. When one is sufficiently fatigued, one may experience microsleeps that can cause them to lose concentration; however, objective cognitive testing should be done to differentiate the neurocognitive deficits of brain disease from those attributable to tiredness. Types Mental fatigue In addition to physical, fatigue also includes mental fatigue, not necessarily including any muscle fatigue. Such a mental fatigue, in turn, can manifest itself both as somnolence (decreased wakefulness) or just as a general decrease of attention, not necessarily including sleepiness. In any case, this can be dangerous when performing tasks that require constant concentration, such as driving a vehicle. For instance, a person who is sufficiently somnolent may experience microsleeps. However, objective cognitive testing should be done to differentiate the neurocognitive deficits of brain disease from those attributable to tiredness. Physical fatigue Physical fatigue or muscle weakness (or "lack of strength") is a direct term for the inability to exert force with ones muscles to the degree that would be expected given the individual's general physical fitness. A test of strength is often used during a diagnosis of a muscular disorder before the etiology can be identified. Such etiology depends on the type of muscle weakness, which can be true or perceived as well as central or peripheral. True weakness is substantial, while perceived rather is a sensation of having to put more effort to do the same task. On the other hand, central muscle weakness is an overall exhaustion of the whole body, while peripheral weakness is an exhaustion of individual muscles. There are seen to be two main types of physical fatigue; Central and Peripheral. * Central Fatigue The central component to fatigue is generally described in terms of a reduction in the neural drive or nerve-based motor command to working muscles that results in a decline in the force output (Gandevia, 2001; Kay et al., 2001; Kent-Braun, 1999; Vandewalle et al., 1991). It has been suggested that the reduced neural drive during exercise may be a protective mechanism to prevent organ failure if the work was continued at the same intensity (Bigland-Ritchie & Woods, 1984; Noakes, 2000). The exact mechanisms of central fatigue are unknown although there has been a great deal of interest in the role of serotonergic pathways (Davis, 1995; Newsholme et al., 1987; Newsholme et al., 1995). * Peripheral Fatigue Fatigue during physical work is considered an ability for the body to supply sufficient energy to the contracting muscles to meet the increased energy demand. This is the most common case of physical fatigue-effecting a national average of 72% of adults in the work force in 2002. This causes contractile dysfunction that is manifested in the eventual reduction or lack of ability of a single muscle or local group of muscles to do work. The insufficiency of energy, i.e. sub-optimal aerobic metabolism, generally results in the accumulation of lactic acid and other acidic anaerobic metabolic by-products in the muscle, causing the stereotypical burning sensation of local muscle fatigue. The fundamental difference between the peripheral and central theories of fatigue is that the peripheral model of fatigue assumes failure at one or more sites in the chain that initiates muscle contraction. Peripheral regulation is therefore dependent on the localised metabolic chemical conditions of the local muscle affected, whereas the central model of fatigue is an intregrated mechanism that works to preserve the integrity of the system by initiating fatigue through muscle derecruitment, based on collective feedback from the periphery, before cellular or organ failure occurs. Therefore the feedback that is read by this central regulator could include chemical and mechanical as well as cognitive cues. The significance of each of these factors will depend on the nature of the fatigue-inducing work that is being performed. Differential diagnosis The majority of people who have fatigue do not have an underlying cause discovered after a year with the condition. In those who do have a possible diagnosis musculoskeletal (19.4%) and psychological problems (16.5%) are the most common. Definitive physical conditions were only found in 8.2%. , in addition to a hint of eye bags, a combination mainly suggestive of minor sleep deprivation.]] Fatigue is typically the result of working, mental stress, overstimulation and understimulation, jet lag or active recreation, depression, and also boredom, disease and lack of sleep. It may also have chemical causes, such as poisoning or mineral or vitamin deficiencies. Massive blood loss frequently results in fatigue. Fatigue is different from drowsiness, where a patient feels that sleep is required. Fatigue is a normal response to physical exertion or stress, but can also be a sign of a physical disorder. The sense of fatigue is believed to originate in the reticular activating system of the lower brain. Musculoskeletal structures may have co-evolved with appropriate brain structures so that the complete unit functions together in a constructive and adaptive fashion. The entire systems of muscles, joints, and proprioceptive and kinesthetic functions plus parts of the brain evolve and function together in a unitary way. Temporary fatigue is likely to be a minor illness like the common cold as one part of the sickness behavior response that happens when the immune system fights an infection. Chronic fatigue, on the other hand, meaning of six months or more duration, is a symptom of a large number of different diseases or conditions. Some major categories of diseases that feature fatigue include: Causes Fatigue is typically the result of working, mental stress, or active recreation, depression, and also boredom, disease and lack of sleep. It may also have chemical causes, such as poisoning or mineral or vitamin deficiencies. The sense of fatigue is believed to originate in the reticular activating system of the lower brain. Musculoskeletal structures may have co-evolved with appropriate brain structures so that the complete unit functions together in a constructive and adaptive fashion. The entire systems of muscles, joints, and proprioceptive and kinesthetic functions plus parts of the brain evolve and function together in a unitary way. Particular cause include: *Lack of sleep(Sleep deprivation perhaps due to sleep disorder) * Addison's disease * Anemia * Arthritis * Autoimmune diseases such as celiac disease, multiple sclerosis, and spondyloarthropathy * Blood disorders such as anemia and hemochromatosis * Cancer * Chronic fatigue syndrome (CFS)*Chronic fatigue syndrome (CFS) * Drug use or Chemical dependency * Depression and other mental disorders that feature depressed mood * Diabetes * Driving fatigue * Eating disorders, which can produce fatigue due to inadequate nutrition * Ejaculatory release * Endocrine disease like diabetes mellitus and hypothyroidism * Endometriosis * Fibromyalgia * Hepatic failure * Headaches * Heart disease * Hyperparathyroidism * Hypothyroidism * Infectious diseases such as infectious mononucleosis and influenza * Jet lag * Leukemia or lymphoma * Lupus erythematosus * Interstitial Cystitis * Malnutrition * Medications, e.g. lithium salts, ciprofloxacin * Metabolic disorders * Mitral valve prolapse/Mitral regurgitation * Mononucleosis * Multiple sclerosis * Muscular Dystrophy * Myasthenia gravis * Neurological disorders such as Parkinson's disease and post-concussion syndrome * Physical trauma and other pain-causing conditions, such as arthritis * Pneumonia * Pregnancy * Primary Biliary Cirrhosis (PBC) * Sleep deprivation, Sleeplessness or sleep disorders * Starvation * Uremia See also *Asthenia *Burnout *Debility *Combat stress reaction (Battle fatigue) *Fatigue and sleep loss during spaceflight *Hypersomnia *Infectious mononucleosis *Kopophobia - fear of being fatigued or exhausted *Malaise *Muscle fatigue *Muscle weakness *Neurological fatigue *Paresis *Sports overtraining *Vigour an antonym References *Bigland-Ritchie, B & Woods, JJ. 1984, 'Changes in muscle contractile properties and neural control during human muscular fatigue'. Muscle Nerve, vol. 7, pp. 691-699. *Cafarelli, E. 1988, 'Force sensation in fresh and fatigued human skeletal muscle'. Exercise and Sport Science Review, vol. 16, pp. 139-168. *Davis, JM. 1995, 'Carbohydrates, branched-chain amino acids, and endurance: the central fatigue hypothesis'. International Journal of Sport Nutrition, vol. 5 Suppl, pp. S29-S38. *Edelman, GM 1989, The remembered present : a biological theory of consciousness. Basic Books, New York. *Enoka, RM & Stuart, DG. 1992, 'Neurobiology of muscle fatigue'. Journal of Applied Physiology, vol. 72, pp. 1631-1648. *Gandevia, SC. 1992, 'Some central and peripheral factors affecting human motoneuronal output in neuromuscular fatigue'. Sports Medicine, vol. 13, pp. 93-98. *Gandevia, SC. 2001, 'Spinal and supraspinal factors in human muscle fatigue'. Physiological Review, vol. 81, pp. 1725-1789. *Gandevia, S. C., Enoka, R. M., McComas, A. J., Stuart, D. G., & Thomas, C. K. 1995, 'Neurobiology of muscle fatigue - Advances and issues'. Advances in Experimental Medicine and Biology, vol. 384. pp. 515-25. *Garner, SH, Sutton, JR, Burse, RL, McComas, AJ, Cymerman, A, & Houston, CS. 1990, 'Operation Everest II: neuromuscular performance under conditions of extreme simulated altitude'. Journal of Applied Physiology, vol. 68, pp. 1167-1172. *Hagberg, M. 1981, 'Muscular endurance and surface electromyogram in isometric and dynamic exercise'. Journal of Applied Physiology, vol. 51, pp. 1-7. *Hawley, JA & Reilly, T. 1997, 'Fatigue revisited'. Journal of Sport Science, vol. 15, pp. 245-246. *Jones, LA & Hunter, IW. 1983, 'Effect of fatigue on force sensation'. Experimental Neurology, vol. 81, pp. 640-650. *Kay, D, Marino, FE, Cannon, J, St Clair Gibson, A, Lambert, MI, & Noakes, TD. 2001, 'Evidence for neuromuscular fatigue during high-intensity cycling in warm, humid conditions'. European Journal of Applied Physiology, vol. 84, pp. 115-121. *Kelso, JAS 1995, Dynamic patterns : the self-organization of brain and behavior. MIT Press, Cambridge, MA. *Kent-Braun, JA. 1999, 'Central and peripheral contributions to muscle fatigue in humans during sustained maximal effort'. European Journal of Applied Physiology, vol. 80, pp. 57-63. *Matthews, PB. 1982, 'Where does Sherrington's "muscular sense" originate? Muscles, joints, corollary discharges?'. Annu.Rev.Neurosci, vol. 5, pp. 189-218. *Newsholme, E. A., Acworth, I. N., & Blomstrand, E. 1987, 'Amino acids, brain neurotransmitters and a functional link between muscle and brain that is important in sustained exercise', in G Benzi (ed.), Advances in Myochemistry, Libbey Eurotext, London, pp. 127-133. *Newsholme, E. A. & Blomstrand, E. 1995, 'Tryptophan, 5-hydroxytryptamine and a possible explanation for central fatigue', in SC Gandevia (ed.), Fatigue, Plenum Press, New York, pp. 315-320. *Noakes, TD. 2000, 'Physiological models to understand exercise fatigue and the adaptations that predict or enhance athletic performance'. Scandinavian Journal of Medicine and Science in Sports, vol. 10, pp. 123-145. *St Clair Gibson, A, Lambert, MI, & Noakes, TD. 2001, 'Neural control of force output during maximal and submaximal exercise'. Sports Medicine, vol. 31, pp. 637-650. *Vandewalle, H, Maton, B, Le Bozec, S, & Guerenbourg, G. 1991, 'An electromyographic study of an all-out exercise on a cycle ergometer'. Arch.Int.Physiol.Biochem.Biophys, vol. 99, pp. 89-93. External links * NIH/Medline * National Cancer Institute * Don't Fall Asleep at the Wheel! Category:Exercise physiology Category:Symptoms